For those trying for the medals, I strongly recommend you be very careful when you are getting near a medal unlock point. Click on High Scores to see what level the game thinks you've gotten up to, which is probably less than the one you've actually gotten up to. Go ahead and close out the game and then when you play it again, it'll penalize you to whatever level it had recorded in the High Scores versus however much further you'd gotten.
You ideally want to get to the exact level as the only level you've played in a run, as you don't want the game running too long as it does seem to have medal disconnect issues, which get likelier the longer it's running and the more the lag builds up.
Also you may want to play just one level past that, until the High Score thinks you are EXACTLY on whatever number (regardless whatever you actually are).
You definitely do not want to do this at an unlucky time such as when Newgrounds happens to go down during a play.
It seems it's a game that's not re-submitting the medals, so you definitely want them to "go through" correctly the first time!